Built-in sink units customarily have at least one sink basin and, in addition, a so-called draining surface which is generally provided with longitudinal ribs extending in longitudinal direction of the sink unit, a circumferential, raised rim as well as, if required, a small basin between sink basin and draining surface, namely a so-called scraps basin, and, finally, often at least one raised, plane area for the attachment of a water outlet fitting, namely a so-called base for tap fittings, which borders on the circumferential, raised rim at the front and/or at the back approximately in the center of the built-in sink unit, in particular. The different surface areas of a sink unit, such as a built-in sink unit, are subject to varying degrees of wear during use: The bottom of the sink basin and the upper sides of the ribs of the draining surface are subjected to particularly hard wear by the bottoms of saucepans or pots, cutlery and the like, the bottom of the scraps basin, the upper side of the base or bases for tap fittings and the upper side of the circumferential, raised rim are also subject to severe wear whereas there is scarcely the risk of other surfaces areas, such as the side walls of the basin and the areas of the draining surface lying deeper than the upper sides of the ribs, being damaged, e.g. scratched, during normal use.
For this reason, in the case of built-in sink units produced from casting resin incorporating filler materials and marketed by the company BLANCO GmbH & Co. KG under the trade name SILACRON, the bottoms of the sink basin and scraps basin, the upper sides of the ribs of the draining surface, the bases for tap fittings and the circumferential, raised rim are provided with a knop-like structure while the remaining surface areas of the visible side of this built-in sink unit, e.g. the side walls of the basin, are smooth and therefore have a high-gloss finish when the sink units are new ("smooth" is to be understood as a surface having a surface roughness which is dependent on the size of the filler particles used and in the known sink units as described amounts to approximately 0.1 .mu.m, whereby the so-called cut-off value was 0.8 mm during testing). Owing to this knop-like structure, scratches, for example, in the bottom of the sink basin are hardly noticeable, and the high-gloss surface areas make the sink units really have the appearance, when new, of being a new article. The knop-like structure is, however, disadvantageous when these sink units are cleaned with abrasive means, and sink units which, like these known SILACRON sink units, have a relatively hard surface can only be cleaned effectively when abrasive means are used: In practice, only the area of the knop tips is, in fact, cleaned so that, for example, unavoidable lime deposits between the knops cannot be effectively removed; even greasy or fatty deposits on the bottom of the sink between the knops are far harder to remove than from the smooth side walls of the sink.
The object underlying the invention was to provide sink units, the optical appearance of which, when new, is really that of a new article, with which the appearance of the surface areas subject to severe wear during use is not essentially impaired over a longer period of time and the surface areas which are subject to severe wear during use can be cleaned effectively and thoroughly with abrasive means.